class Solution {
public:
  int climbStairs(int n) {

    int dp[n + 3];
    dp[1] = 1;
    dp[2] = 2;

    for(int i = 3; i <= n; ++i){
      dp[i] = dp[i - 1] + dp[i - 2];
    }

    return dp[n];

  }
};